1. Field of the Invention
The present invention generally relates to a vehicular coupler and, more particularly, to a shock absorber for use with a coupler for coupling vehicles such as trains.
2. Description of the Prior Art
In the prior art, rubber shock absorbers have been used for vehicular couplers because they are small and light, but enjoy a large shock absorbing capacity, a low cost and excellent maintainability. Since rubber has non-linear recessed load-deformation characteristics, it has a small shock absorbing capacity within a low-load range, in which shocks applied are weak, so that it can enjoy a high cushioning effect. When the shocks become strong, on the contrary, the rubber has such characteristics that it has a low cushioning effect but can enjoy a large shock absorbing capacity.
The rubber shock absorber is initially pressurized to some extent to compensate for its so-called "yield" due to aging of the rubber after a long use. As a result, the shock absorber exhibits a predetermined performance if it is subjected to a pressure equal to or stronger than the initial one, but not if the pressure applied is weaker than the initial one.
To solve this problem, it has been stated in JA-OS Nos. 54-138213 and 54-138214, laid open for public inspection on Oct. 26, 1979, to use a shock absorber in which two elastic members of rubber are used to interpose an H-shaped shock absorbing frame inbetween so that they may offset their initial pressures. The shock absorber disclosed in the above cited references is intended to enjoy a shock absorbing effect even for a low load of weak shocks. However, this prior art shock absorber raises new problems in that it requires two sets of main elastic members, whereas other prior art shock absorbers are equipped with only one. As a result, consideration has to be taken into the tensile direction of elasticity, whereas only the elasticity in the direction of compression had been considered in other prior art shock absorbers. Hence a compression range of the elastic member twice as high as that of the prior art is required to construct the elastic member, typically by overlaying rubber pads having complicated shapes. Also there is a fear of the aging of the rubber elastic member.